Analysis of ZDR Columns to Aid Severe Weather Forecasting

Dual-Polarization (Dual-Pol) technology has many tools to help with nowcasting during severe weather events and Differential Reflectivity (ZDR) columns are among one of its many advantages. ZDR columns are an area of positive ZDR values extending above the environmental freezing level. This allows for a visualization of the location of updrafts capable of lofting liquid water droplets above the freezing level. ZDR columns are currently able to help determine relative updraft strength and the possibility of storm splitting. In this research, four severe weather cases were analyzed to see if ZDR columns could potentially help with the understanding and predictability of severe weather forecasting. Level 2 base radar data was analyzed to study how ZDR columns evolved prior to a severe report. These changes were examined based on height, strength, location and shape of the column as it changed with time. A couple of trends in the ZDR columns were present with each storm that produced severe reports. This study showed that ZDR column height fluctuations prior to producing a tornado. A second trend was that a U shaped ZDR column was common in storms well before producing a tornado. This work shows promise to give operational forecasters another tool when forecasting severe weather, especially tornadoes, by analyzing ZDR columns.